The present invention relates to methods and devices for withdrawing body fluid in which a lancing element is inserted into the skin of a body part and body fluid is collected by a capillary structure of the lancing element.
Methods and devices are known for withdrawing small amounts of body fluid and are used by diabetics to self-monitor their blood sugar several times daily. These corresponding methods and devices are directed toward a disposable measuring microneedle disposed in a hand-held device to generate a skin puncture, to remove a small amount of blood using capillary forces, and to analyze the blood sample. With this type of integrated system, a layperson can simply and rapidly carry out the necessary steps during a substantially automated measuring process. In order to achieve this, however, it is important that the lancing and collecting processes are adapted to the disposable microneedle such that blood or other body fluid can be collected efficiently, rapidly and without causing significant pain to the user.
To meet these goals, known devices may detect when the skin is contacted in order to achieve a defined lancing depth for the control of the forward-directed lancing movement. However, such movement control has to be adapted to the desired lancing speed using a very complex apparatus. Additionally, such a system cannot be used to provide information about the actual success of the blood collection.
In order to optimize the collection of blood samples, document WO 03/009759 describes a method in which a puncture is made and the lancing unit, having a capillary structure, is then retracted along a portion of the lancing path and is left there for a few seconds to collect the sample. This opens a portion of the lancing channel such that body fluid can collect therein and subsequently enter the capillary structure.
A lancing system described in document WO 2004/080306 detects a characteristic parameter (e.g., impedance) during the lancing movement and optionally during the retraction. This detection only serves as a skin detection in order to indicate the penetration depth, penetration stability, or residence time (i.e., duration of penetration and retraction) for the user.